scheme 3

IPI (2.60g), dimethylthexylsilyl chloride (5.36g) and triethylamine 5.0g) in DMF (50mL) were heated at 90 C under nitrogen overnight. The cooled solution was diluted with ice-water (~200mL) and the N,N'-bis-dimethylthexylsilyl-IPI [bis-dmt-IPI] collected (4.40g, 79%). White crystals from ethyl acetate, m.p. 217-8 C. Similar derivatives of PIPI (86%, m.p. 285-8 C) and IPIPIPI (85%, m.p. >340 C) both recrystallised from toluene.
IPI (2.47g, 0.01mol) and 2,6-difluoropyridine (2.79g, 0.024mol) in THF( 0mL) containing NaH (1.20g, 50%, 0.025mol) were heated at reflux for 40h under nitrogen and the poured into water to give FPIPIPF as white crystals from DMF, m.p. 318-9 C.
Bis-dmt-IPI (4.26g), t-Bu-IP and cesium fluoride (0.2g) in DMF (100mL) were heated at 110 C for 2 days, cooled and poured into water. The filtered product, bis-t-Bu-IPIPIPI (4.80g, 88%) produced white crystals from toluene m.p. >340 C. This product with 20% aqueous HCl at 80 C overnight gave IPIPIPI (91%), m.p. >340 C.
PIP (8.28g, 0.03mol) and N-t-butylimidazolidinone (9.37g,0.066mol) in THF containing NaH (3.20g, 50%, 0.067mol) were refluxed for 48h under nitrogen. Most of the solvent was removed and ice-water (~500mL) added to reprecipitate bis-t-Bu-IPIPI which recrystallised from toluene (12.6g, 81%) m.p. 298-9 C. Heating this compound (8.20g) in HCl (80mL, 20% aqueous) at 100 C overnight gave IPIPI (6.31g, 98%) which recrystallised from aqueous TFA, m.p. >300 C.